Method for optical measurement of the three dimensional geometry of objects

Abstract

The invention relates to a method for optically scanning the three-dimensional geometry of an object by means of triangulation, in which a pattern (9, 9′) is projected onto the object (7) to be scanned in order to obtain a 3D data set, and the projected pattern (9, 9′) is recorded in an image (40, 41). In a first step for the production of at least one first image (40), a first pattern (9) is projected and in a second step for the creation of at least one further image (40), a further pattern (9′) deviating from the first as regards position or shape is projected onto the object (7) to be scanned and the image (41) is created. The first image (40) and the further image (41) comprise at least one common point (44). The 3D data acquired from the images (40, 41) are merged in a subsequent step on the basis of the 3D data of the at least one common point (44) such that the 3D data acquired from said images (40, 41) agree at least with reference to the 3D data of the common point (44) in the 3D data set.

Description

TECHNICAL FIELD[0001]The invention relates to a method for optical measurement of the three dimensional geometry of objects and is concerned with the problem of camera-shake induced in 3D data of scanned objects acquired using stripe projecting methods and with the task of 3D scanning when there is relative motion between the camera and the object when being scanned, particularly for dental purposes.PRIOR ART[0002]Digital design data for the computer-assisted production of dental prosthetic items without having to create the usual impression can be acquired by optically scanning one or more teeth in a patient's mouth.[0003]For such scanning, use is frequently made of measuring methods based on the principle of triangulation. Phase-shifting triangulation is disclosed in EP 0 160 797, in which a three dimensional data set is acquired from a sequence of images of a pattern which is displaced from image to image.[0004]With prior triangulation methods, a single straight stripe of light i...

AI Technical Summary

Benefits of technology

[0035]One advantage of this method of the invention is that, unlike conventional methods, it corrects the errors that are caused by shaking movements of the hand-held scanning device. This is especially advantageous for dental intra-oral cameras, which are hand-held and used to generate 3D data sets of tooth surfaces. Camera-shake causes the resulting 3D images to show defects such as pointed or stepped structures, and the 3D scan must be repeated.

[0036]The overlapping of the common points allows the changes in position of the pattern caused by camera-shake to be identified and compensated for.

[0037]Another advantage is that the method of the invention makes on-the-fly measurement possible. The scanning device can be moved smoothly relatively to the object being scanned and the individual images scanned from different directions can be combined to form a complete 3D data set. It is thus not necessary to hold the scanning device still during an exposure. A sequence of exposures can be made without interruption while the scanning device is being moved relatively to the object.

Problems solved by technology

Since the change in the orientation between camera and object is, however, unknown, the two-dimensional patterns of the images Pi cannot be correctly merged to form a common 2-dimensional pattern of the overall image, which, for example, is chosen so as to be the same as the coordinate system of the first exposure.

When the relief data contained in the lines of the 2-dimensional patterns of the blurred individual images are merged to form a common 2-dimensional pattern, an erroneous surface structure of the object being scanned will be obtained.

The present problem is to provide a method for creating a three-dimensional image of an object being scanned, particularly for dental purposes, which produces a sufficiently accurate 3D model even if camera-shake takes place.

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